1. Field of the Invention
The invention relates to pivotal connections, and in particular to a pivotal mounting assembly which provides both a smooth, low-friction, sliding and shock-absorbing connection between a pair of movable members. More particularly, the invention relates to an improved pivotal mounting assembly primarily for use with the shoes of a centrifugal clutch.
2. Description of the Prior Art
There are numerous types and arrangements of pivot connections or pivotal mounting assemblies for a pair of members, one of which is adapted to swing or pivot with respect to the other member. One common type of pivot assembly consists of a cylindrical pivot pin or projection which is telescopically mounted on or engaged within a complementary-shaped opening formed in the other member. These pivot pins, depending upon the particular assembly in which they are used, are either formed of metal when relatively large forces and stresses are exerted thereon, or they may be formed of plastic or similar synthetic materials when the exerted forces are relatively small.
Clutches, brakes, and similar types of equipment have one or more members, referred to as "shoes", which are pivotally mounted on a supporting member which is either fixed or rotatable with respect to the specific type of equipment with which it is to be used. These shoes pivot outwardly when acted upon by some means to couplingly engage an outer member or housing so that the members will rotate in unison, as in a clutch construction, or will stop further rotation of the members, as in a brake assembly. The shoes, and in particular, the pivotal mounting assembly therefor, will experience relatively large forces and stresses or a plurality of vibrational stresses upon and during coupling engagement with the outer member. Unless the pivotal mounting assembly is formed of sufficiently rigid materials, failure will ultimately result requiring replacement or undesirable maintenance.
It is desirable that the pivotal mounting arrangement for many of these shoes be provided with some type of shock-absorbing feature or component which assists in lessening the coupling forces and stresses exerted on the shoes and pivot pins. Various types of resilient bushing arrangement have been used for mounting of brake and clutch shoes. One particular type of assembly consists of a cylinder or annulus of an elastomer or synthetic material which is telescopically mounted on and surrounds a metal pivot pin with the shoe being pivotally mounted thereon. This intervening annulus or layer of shock-absorbing material absorbs many of the forces and stresses exerted on the inner metal pin and adjacent shoe areas. These types of cushioned pivotal mounting arrangements have the disadvantage of increasing the outer diameter of the pivot pin since the inner metallic pin is completely surrounded by the annulus of resilient material. The inner steel pin is required for strength of the pivot with the outer resilient layer providing the shock-absorbing effect, and in some assemblies a low-friction sliding surface.
Such assemblies have the further disadvantage of requiring greater thicknesses of shock-absorbing material than may be desirable in order to withstand the stresses which are exerted thereon since the exerted forces compress the affected areas of the resilient layer toward the inner steel pin. The adjacent areas are forced or bulged outwardly since they are unrestrained. This can result in rupture or cracking of the adjacent areas of resilient material. Also, it is difficult to prevent the resilient annulus from turning on the inner fixed metal pin, which results in high wear rates.
These known types of shock-absorbing pivotal mounting assemblies can be properly designed to, and in many constructions do, provide satisfactory results. However, such assemblies require larger components than desirable, and space is at a premium in most clutch and brake constructions and similar types of equipment.
Therefore, the need has existed for an improved pivotal mounting assembly intended primarily for use in clutches, brakes and similar equipment, for the mounting of shoes therein which will absorb the various impact forces and stresses exerted on the pivot assembly which are experienced when the shoes couplingly engage an outer member, and which will provide a smooth, reduced friction sliding surface for the pivotal movement of the shoes.
No assembly of which I am aware achieves these results by using an insert strip preferably formed of a high strength plastic material in combination with the surrounding metal to provide the required strength as well as shock-absorbing ability for the pivot assembly.